We are investigating the DNA-cytosine methylases controlled by the N-3-drug-resistance (R) factor and by the host E.coli K12 mec plus gene. We have demonstrated that the two enzymes may be related and will try to compare the sequences of residues in the pyrimide tracts containing the 5-methylcytosine (MeC). In addition to comparing the site specificity, we will be purifying the respective enzymes in order to investigate possible similarity at the protein level.